Liquid for removing printing and screen printing inks: butyrolactone and/or N-methyl-2-pyrrolidone and propylene glycol derivative

ABSTRACT

A liquid for removing printing and screen printing inks comprising an essentially anhydrous mixture containing: 
     (a) q-butyrolactone and/or N-methyl-2-pyrrolidone in an amount of 1-25% (v/v); 
     (b) one or more propylene glycol derivatives selected from substituted propyl acetates and/or propylene glycol ethers; and optionally 
     (c) a diluent selected from aliphatic compounds having a flash point above 22° C. and a content of aromatic compounds below 1%; and/or 
     (d) a surfactant, the amount of components (b), (c) and (d) constituting 99-75% (v/v) of the liquid.

The present invention concerns a liquid for removing printing and screenprinting inks, in particular for cleaning screen printing frames.

The liquid of the invention, which is useful in solving all types ofcleaning problems in the printing and screen printing industry withoutthe use of dangerous substances, is characterized by consisting of anessentially anhydrous mixture comprising

(a) γ-butyrolactone of the formula ##STR1## and/orN-methyl-2-pyrrolidone of the formula ##STR2## in an amount of 1-25%,preferably about 10% (v/v) as well as

(b) one or more propylene glycol derivatives selected among substitutedpropyl acetates of the general formula ##STR3## wherein R is hydrogen oralkyl having from 1 to 6 carbon atoms, and/or propylene glycol ethers ofthe general formula ##STR4## wherein R₁ is alkyl having from 1 to 6carbon atoms, and n is 1, 2 or 3, and optionally

(c) a diluent selected among aliphatic compounds having a flash pointabove 22° C. and a content of aromatic compounds below 1% and/or

(d) a surfactant, the amount of components (b), (c) and (d) constituting99-75% (v/v) of the liquid.

Dilution as well as universal cleaning or washing of printing and/orscreen printing inks from stencils, printing plates, screen printingframes, rollers and the like was previously made by means of cleaningliquids, which either contain "dangerous substances", cf. e.g. thenotice no. 147 issued by the Environmental Protection Agency on Mar. 16,1981, or aromatic solvents the use of which involves considerable riskto the individuals working with these agents. In particular for thecleaning of old dried-up ink residues in offset and letterpressprinting, mainly xylene- and toluene-based agents were used in the past,whose health effects are well-known. To this should be added that theknown cleaning liquids frequently exhibit very low flash points, whichpartly entails that the liquids predominantly ignite easily, and partlymay be an expression of a high volatility and thus increased potentialhealth risk through aspiration of vapours. Thus, toluene has a flashpoint of only 5° C.

The currently leading cleaning liquid for washing screen printing framesis thus "Pregan 240E" from Kissel & Wolf, West Germany, which has thefollowing composition:

Ethyl acetate: 10%

Isobutyl acetate: 32%

"Solvesso 100": 58%

and a flash point of 31° C.

"Solvesso 100" from Esso Chemicals contains 99% aromates.

It has long been known that the diluent liquids for ink formulationsrecommended by the ink manufacturers, are based on solvents whichcontain dangerous substances and therefore require utmost care.

As regards the cleaning process, the task is even more difficult. Here,dried-up inks are often to be dissolved in order for these to be removedfrom the printing and screen printing apparatus. Some inks are easy toremove, while others are extremely difficult to handle, and the inktypes used are moreover different at the individual graphic firms. Someinks are extremely pernicious because they consist of two-componentsystems. Such inks may be difficult to remove within an ordinary workingday, unless cleaning liquids of a type involving health dangers areused.

Consequently, it was necessary in the past to keep the above-mentioneddangerous and easily ignitable cleaning liquids, because only suchliquids have been found to be able to dissolve all the ink types in use.

The screen printing industry faces particular problems because thecleaning liquids able to remove all inks also tend to destroy the gluewhich is used in the mounting of screens on screen printing frames.Further, it is not possible to select water-based or stronglyhydrophilic cleaning liquids at will because such liquids will tend todestroy the stencil emulsion.

The use of γ-butyrolactone and/or N-methyl-2-pyrrolidone as a cleaningagent for printing inks is known. Thus, such use is described in the FRPatent Specification No. 2,354,377, but this specification deals withremoval of the stencil itself and not the printing ink. An importantproperty of a cleaning agent for removal of screen printing inks is thatit does not remove or destroy the stencil. The cleaning agent accordingto the mentioned FR specification contains e.g. periodate ions whichdestroy stencils based on polyvinyl alcohol. The agent may moreovercontain large amounts of water which will also be harmful to the stencilused.

A cleaning liquid predominantly consisting of N-methyl-2-pyrrolidone ismentioned in the EP Patent Specification 21149. However, this liquidprimarily serves to dissolve polyurethane and epoxy lacquers, which itis intended to avoid with the cleaning liquid of the invention becausethe glue used for the mounting of screen printing frames is made on thisbasis.

The DE Offenlegungsschrift No. 3,401,982 concerns water-based printinginks with a pH of 9-11, which may contain solvents, such asN-methyl-2-pyrrolidone, to improve the solubility of the ink in theformulation. The cleaning liquids comprised by the invention, however,are not water-based, but are in contrast essentially anhydrous since, asmentioned, water in large amounts will degrade the stencils used inpractice.

A lacquer remover based on γ-butyrolactone is known from the U.S. PatentSpecification No. 2,438,038. This lacquer remover, however, is alsowater-based, and it moreover contains from 40 to 80% γ-butyrolactone orγ-valerolactone whereas the liquid of the invention does not containsubstantial amounts of water and may have a maximum content of 25%γ-butyrolactone since, otherwise, it would decompose the glue. In otherwords, the cleaning liquid known from this U.S. specification cannot beused for cleaning screen printing frames while maintaining both the glueand the stencil.

The EP Application 81355 describes a process and an agent for cleaningprinting screens. The agent of the EP application requires the use ofN-methyl-2-pyrrolidone in amounts of 30-85%, which will causedecomposition of the polyurethane-based and epoxy-based glue types usedin the screen printing for mounting of screens. Further, the agent ofthe mentioned EP application may contain cyclohexanone or halogenatedcompounds, which are termed dangerous substances and which are notincluded in the liquid of the invention.

As will appear from a following example, glue systems based ontwo-component epoxy or polyurethane will be decomposed and rendereduseless, if the screen printing frames when being cleaned of inks aresubjected to cleaning liquids whose formulations include more than 25%γ-butyrolactone or N-methyl-2-pyrrolidone.

The ability of a solvent to dissolve a given substance, e.g. a polymer,may conveniently be evaluated by parameter considerations according tothe so-called "Hansen system", which is described in Encyclopedia ofChemical Technology, Suppl. vol. 2nd Ed., p. 889-910, John Wiley & Sons,New York, and by Charles M. Hansen in Farg Och Lack 17, 69-77 (1971).According to the "Hansen system", a solvent may be described by threesolubility parameters δ_(D) (dispersion parameter), δ_(P) (polarityparameter) and δ_(H) (hydrogen bonding parameter), whose squares incombination are the square of the total cohesive energy:

    δ.sub.tot.sup.2 =δ.sub.D.sup.2 +δ.sub.P.sup.2 +δ.sub.H.sup.2.

Two substances have a maximum interaction (i.e. are soluble in eachother) when their solubility parameters in pairs are as close to eachother as possible. A solvent may thus be characterized by a totalparameter which may be divided into three sub-parameters, which may e.g.be illustrated in a three-dimensional system of co-ordinates with thesub-parameters as axes.

The solubility of polymers, e.g. such as are used as binders in printinginks, may accordingly be characterized on the basis of their interactionwith different solvents, it having been found that all solvents capableof dissolving a specific binder are within a defined volume in theabove-mentioned system of co-ordinates. If the scale on the δ_(D) axisis expanded by a factor of 2, the solubility range will be a ball. Apolymer may thus be characterized by a centre (δ_(D), δ_(P), δ_(H)) anda radius R_(P).

Any solvent can be adapted to the three-dimensional system ofco-ordinates for a given polymer on the basis of its three parameters.It is determined subjectively by solubility tests whether the individualsolvent can dissolve the polymer or not, and the solubility range of thepolymer is then determined by electronic data processing, the programiteratively determining a centre and a radius, so that the greatestpossible number of active solvents is within the resulting ball, whilethe inactive agents are outside it.

It is described in the following examples 1 and 2 how possible solventshave been found by means of the "Hansen system" for two ordinaryprinting inks, "Thermojet Hvid" and "Drugloss Blå", which are consideredto be some of the most difficult inks to remove from printing equipment.Examples 3-6 describe similar calculations for four additional ordinaryprinting inks which are difficult to remove.

However, it has been found by a methodical examination of commerciallyavailable screen printing and printing inks with a view to developingnew cleaning and diluting liquids that Hansen's parameter theory, noteven in case of equilibrium without regard to the time parameter, leadsto unambiguous results. Possible explanations are i.a. that the inks maybe complicated and contain several polymers, and that the parametermodel is complicated by the use of mixtures of solvents. Moreover, inpractice, it is necessary to consider the abovementioned "time factor"because a solvent is not useful in practice, if it is active only afterexposure for an extended period of time, even though it satisfies theHansen model.

Accordingly, to obtain results which are useful in practice, it isnecessary to use a modified Hansen model to find a solvent which initself can dissolve the inks in question, but which--to obtain areasonably high dissolution rate and suitable low costs--is included ina mixture of one or more other agents.

It has surprisingly been found that the cleaning liquid of the inventionis capable of dissolving all printing and screen printing inks which areused in practice. The subject liquid mixtures consist of compounds,which each are used as solvents for a number of purposes, and which arecharacterized by suitably high flash points, just as they involve anappropriately small health risk in use, see e.g. Paint & Resin 53 (5),42-47 (1983).

N-methyl-2-pyrrolidone and γ-butyrolactone are, as mentioned, solventseach of which or in mutual mixtures have been found to be capable ofdissolving many, but not all ordinary printing and screen printing inks.Thus, e.g. γ-butyrolactone cannot dissolve Colorjet CO113 mandarinorangefrom Sericol (see example 3), and N-methyl-2-pyrrolidone cannot dissolveSeristar SX (see example 4). Therefore, it has been found necessary toadd one or more substituted propyl acetates or propylene glycol etherssince this results in (a) solubility, (b) higher dissolution rates (i.e.improved time parameters) in several cases and (c) economically moreadvantageous cleaning liquids.

γ-Butyrolactone and/or N-methyl-2-pyrrolidone (a) is to be mixed withsuch substituted propyl acetates or propylene glycol ethers (b) withincertain limits which are determined in view of such conditions assolubility, dissolution rate ("time parameter") and economy. The bestresults, also economically, are obtained when the mixture ratio of (a)to (b) is between 25:75 and 1:99 (v/v).

The subject liquid may contain as component (b) e.g. propyl acetatesand/or one or more propylene glycol ethers selected among propyleneglycol monomethyl ether, propylene glycol monoethyl ether, dipropyleneglycol monomethyl ether and tripropylene glycol monomethyl ether. Thediluent (c) may e.g. be butyl diglycol ether, ethyl diglycol ether ormethyl diglycol ether, or it may be one or more aliphatic hydrocarbons.The type and amount of the diluent are selected in view of the flashpoint of the mixture, which must not be below 22° C. Preferably, theflash point should be above 55° C.

Moreover, the subject liquid may contain a surfactant, in particular anon-ionic surfactant (d), preferably in the form of a nonylphenolethoxylate.

As mentioned, the subject liquids may be used for all types of cleaningtasks in the screen printing and printing field. In the screen printingfield, the liquids are particularly used for cleaning frames, but alsoduring the actual printing process. In offset, the liquids may be usedfor cleaning old dried-up ink residues and for cleaning machine parts,rollers, plates, etc.

As mentioned, component (a) may constitute up to 25% of the mixture.Components (c) and (d) together may constitute up to 50% of the mixture.Otherwise, the mixture may be composed within rather wide limits withrespect to the specific field of use.

The invention will be illustrated more fully by the following examples.

EXAMPLE 1

In this example possible solvents for the printing ink "Thermojet Hvid"are selected on the basis of solubility tests and Hansen parameters. Theability of the selected solvents to dissolve the ink is evaluatedsubjectively, the solubility tests being performed in test tubes inwhich the ink is in contact with an excess of the liquids in question.The evaluation is made after 10 minutes and after 24 hours.

The results obtained are listed in the following table 1, from which iti.a. appears that some of the solvents require long-term exposure beforethey are active.

                  TABLE 1                                                         ______________________________________                                        Solubility range for "Thermojet Hvid"                                         δ.sub.D = 18.77 δ.sub.P = 11.55 δ.sub.H = 7.81 R.sub.P      = 9.76                                                                                             Solubility                                               Solvent       δ.sub.D                                                                        δ.sub.P                                                                        δ.sub.H                                                                      10 min.                                                                              24 hours                              ______________________________________                                        Acetone       15.50  10.40  7.00 yes.sup.a                                                                            --                                    Acetophenone  19.60  8.60   3.70 no.sup.b                                                                             yes                                   1,3-butane diol                                                                             16.60  10.00  21.50                                                                              no     no                                    Butyl acetate 15.80  3.70   6.30 no     yes.sup.a                             γ-butyrolactone                                                                       19.00  16.60  7.40 yes    --                                    Carbontetrachloride                                                                         17.80  0.00   0.60 no     no                                    Chlorobenzene 19.00  4.30   2.00 yes.sup.a                                                                            --                                    Chloroform    17.80  3.10   5.70 yes    --                                    Cyclohexanol  17.40  4.10   13.50                                                                              no     no.sup.b                              Diacetone alcohol                                                                           15.80  8.20   10.80                                                                              no.sup.b                                                                             yes                                   o-dichlorobenzene                                                                           19.20  6.30   3.30 no.sup.b                                                                             yes                                   Diethylene glycol                                                                           16.20  14.70  20.50                                                                              no     yes.sup.a                             Diethyl ether 14.50  2.90   5.10 no     no                                    Dimemethyl formamide                                                                        17.40  13.70  11.30                                                                              yes.sup.a                                                                            --                                    Dimethyl sulfoxide                                                                          18.40  16.40  10.20                                                                              no     yes                                   1,4-dioxane   19.00  1.80   7.40 no     yes.sup.a                             Dipropylene glycol                                                                          15.90  20.20  18.40                                                                              no     no                                    Ethanol       15.80  8.80   19.40                                                                              no     no                                    Ethyl acetate 15.80  5.30   7.20 yes    --                                    Ethylene dichloride                                                                         19.00  7.40   4.10 yes    --                                    Ethylene glycol                                                                             17.00  11.00  26.00                                                                              no     no                                    Ethylene glycol mono-                                                                       15.90  4.70   10.60                                                                              no     yes                                   ethyl ether acetate                                                           Hexane        14.90  0.00   0.00 no     no                                    Isophorone    16.90  8.20   7.40 no.sup.b                                                                             yes                                   Methanol      15.10  12.30  22.30                                                                              no     no                                    Methylene chloride                                                                          18.20  6.30   6.10 yes    --                                    Methyl isobutyl ketone                                                                      15.30  6.10   4.10 no     yes                                   N--methyl-2-pyrro-                                                                          18.00  12.30  7.20 yes    --                                    lidone                                                                        Nitrobenzene  20.00  8.60   4.10 no     yes                                   2-nitropropane                                                                              16.20  12.10  4.10 no     yes                                   Propylene carbonate                                                                         20.00  18.00  4.10 *      yes                                   Propylene glycol                                                                            16.80  9.40   23.30                                                                              no     no                                    Tetrahydrofuran                                                                             16.80  5.70   8.00 yes    --                                    Toluene       18.00  1.40   2.00 no     no                                    Trichloroethylene                                                                           18.00  3.10   5.30 yes    --                                    ______________________________________                                         *Not evaluated after 10 min.                                                  .sup.a Ought to have been within the calculated ball                          .sup.b Ought to have been outside the calculated ball                    

EXAMPLE 2

Like in example 1, possible solvents for the printing ink "Drugloss Blå"are selected on the basis of solubility tests and Hansen parameters.

The results obtained are listed in table 2:

                  TABLE 2                                                         ______________________________________                                        Solubility range for "Drugloss Bla"                                           δ.sub.D = 17.54 δ.sub.P = 8.35 δ.sub.H = 7.33 R.sub.P =     5.90                                                                                               Solubility                                               Solvent       δ.sub.D                                                                        δ.sub.P                                                                        δ.sub.H                                                                      10 min.                                                                              24 hours                              ______________________________________                                        Acetone       15.50  10.40  7.00 yes    --                                    Acetophenone  19.60  8.60   3.70 yes    --                                    1,3-butanediol                                                                              16.60  10.00  21.50                                                                              no     no                                    1-butanol     16.00  5.70   15.80                                                                              no     no                                    Butyl acetate 15.80  3.70   6.30 yes.sup.a                                                                            --                                    γ-butyrolactone                                                                       19.00  16.60  7.40 yes    --                                    Carbontetrachloride                                                                         17.80  0.00   0.60 no     no                                    Chlorobenzene 19.00  4.30   2.00 yes.sup.a                                                                            --                                    Cyclohexanol  17.40  4.10   13.50                                                                              no     no                                    Diacetone alcohol                                                                           15.80  8.20   10.80                                                                              no.sup.b                                                                             yes                                   o-dichlorobenzene                                                                           19.20  6.30   3.30 no.sup.b                                                                             yes                                   Diethylene glycol                                                                           16.20  14.70  20.50                                                                              no     no                                    Diethyl ether 14.50  2.90   5.10 no     no                                    Dimemethyl sulfoxide                                                                        18.40  16.40  10.20                                                                              no     yes                                   1,4-dioxane   19.00  1.80   7.40 no     yes.sup.a                             Dipropylene glycol                                                                          15.90  20.20  18.40                                                                              no     no                                    Ethanol       15.80  8.80   19.40                                                                              no     no                                    Ethyl acetate 15.80  5.30   7.20 yes    --                                    Ethylene dichloride                                                                         19.00  7.40   4.10 yes    --                                    Ethylene glycol                                                                             17.00  11.00  26.00                                                                              no     no                                    Ethylene glycol mono-                                                                       15.90  4.70   10.60                                                                              yes    --                                    ethyl ether acetate                                                           Hexane        14.90  0.00   0.00 no     no                                    Isophorone    16.90  8.20   7.40 no.sup.b                                                                             yes                                   Methanol      15.10  12.30  22.30                                                                              no     no                                    N--methyl-2-pyrro-                                                                          18.00  12.30  7.20 yes    --                                    lidone                                                                        Nitrobenzene  20.00  8.60   4.10 no     yes                                   2-nitropropane                                                                              16.20  12.10  4.10 no.sup.b                                                                             yes                                   Propylene glycol                                                                            16.80  9.40   23.30                                                                              no     no                                    Toluene       18.00  1.40   2.00 no     yes.sup.a                             Trichloroethylene                                                                           18.00  3.10   5.30 yes    --                                    ______________________________________                                         .sup.a Ought to have been within the calculated ball                          .sup.b Ought to have been outside the calculated ball                    

EXAMPLE 3

Like in example 1, possible solvents for the printing ink "Color Jet"are selected on the basis of solubility tests and Hansen parameters.

The results obtained are listed in table 3:

                  TABLE 3                                                         ______________________________________                                        Solubility range for "Color Jet" (CO-113)                                     δ.sub.D = 14.34 δ.sub.P = 7.45 δ.sub.H = 10.12 R.sub.P      = 12.75                                                                                            Solubility                                               Solvent       δ.sub.D                                                                        δ.sub.P                                                                        δ.sub.H                                                                      10 min.                                                                              24 hours                              ______________________________________                                        Acetone       15.50  10.40  7.00 yes    --                                    Acetophenone  19.60  8.60   3.70 yes    --                                    1,3-butane diol                                                                             16.60  10.00  21.50                                                                              no.sup.b                                                                             no.sup.b                              1-butanol     16.00  5.70   15.80                                                                              yes    --                                    Butyl acetate 15.80  3.70   6.30 yes    --                                    γ-butyrolactone                                                                       19.00  16.60  7.40 no     no                                    Carbontetrachloride                                                                         17.80  0.00   0.60 yes.sup.a                                                                            --                                    Chlorobenzene 19.00  4.30   2.00 yes.sup.a                                                                            --                                    Chloroform    17.80  3.10   5.70 yes    --                                    Cyclohexanol  17.40  4.10   13.50                                                                              no.sup.b                                                                             no.sup.b                              Diacetone alcohol                                                                           15.80  8.20   10.80                                                                              yes    --                                    o-dichlorobenzene                                                                           19.20  6.30   3.30 yes    --                                    Diethylene glycol                                                                           16.20  14.70  20.50                                                                              yes.sup.a                                                                            --                                    Diethylene glycol                                                                           16.00  7.00   10.60                                                                              yes    --                                    monobutyl ether                                                               Diethyl ether 14.50  2.90   5.10 yes    --                                    Dimemethyl formamide                                                                        17.40  13.70  11.30                                                                              yes    --                                    Dimethyl phthalate                                                                          18.60  10.80  4.90 yes    --                                    Dimethyl sulfoxide                                                                          18.40  16.40  10.20                                                                              no.sup.b                                                                             no.sup.b                              1,4-dioxane   19.00  1.80   7.40 yes    --                                    Dipropylene glycol                                                                          15.90  20.20  18.40                                                                              no     no                                    Dipropylene glycol                                                                          15.50  5.70   11.20                                                                              yes    --                                    methyl ether                                                                  Ethanol       15.80  8.80   19.40                                                                              yes    --                                    Ethyl acetate 15.80  5.30   7.20 yes    --                                    Ethylene dichloride                                                                         19.00  7.40   4.10 yes    --                                    Ethylene glycol mono-                                                                       15.90  4.70   10.60                                                                              yes    --                                    ethyl ether acetate                                                           Hexane        14.90  0.00   0.00 no.sup.b                                                                             no.sup.b                              Isophorone    16.90  8.20   7.40 yes    --                                    Methanol      15.10  12.30  22.30                                                                              yes.sup.a                                                                            --                                    Methylene chloride                                                                          18.20  6.30   6.10 yes    --                                    N--methyl-2-pyrro-                                                                          18.00  12.30  7.20 yes    --                                    lidone                                                                        Nitrobenzene  20.00  8.60   4.10 yes.sup.a                                                                            --                                    2-nitropropane                                                                              16.20  12.10  4.10 yes    --                                    Propylene carbonate                                                                         20.00  18.00  4.10 no     no                                    Propylene glycol mono-                                                                      15.60  6.30   11.60                                                                              yes    --                                    methyl ether                                                                  Tetrahydrofuran                                                                             16.80  5.70   8.00 yes    --                                    Toluene       18.00  1.40   2.00 yes    --                                    Trichloroethylene                                                                           18.00  3.10   5.30 yes    --                                    ______________________________________                                         .sup.a Ought to have been within the calculated ball                          .sup.b Ought to have been outside the calculated ball                    

EXAMPLE 4

Like in example 1, possible solvents for the printing ink "Seristar SX"are selected on the basis of solubility tests and Hansen parameters.

The results obtained are listed in table 4:

                  TABLE 4                                                         ______________________________________                                        Solubility range for Sericol red Seristar D2528                               δ.sub.D = 16.25 δ.sub.P = 14.43 δ.sub.H = 10.29 R.sub.P     = 11.06                                                                                            Solubility                                               Solvent       δ.sub.D                                                                        δ.sub.P                                                                        δ.sub.H                                                                      10 min.                                                                              24 hours                              ______________________________________                                        Acetone       15.50  10.40  7.00 yes    --                                    Acetophenone  19.60  8.60   3.70 yes.sup.a                                                                            --                                    1,3-butane diol                                                                             16.60  10.00  21.50                                                                              no     no                                    1-butanol     16.00  5.70   15.80                                                                              no     no                                    Butyl acetate 15.80  3.70   6.30 yes.sup.a                                                                            --                                    γ-butyrolactone                                                                       19.00  16.60  7.40 yes    --                                    Carbontetrachloride                                                                         17.80  0.00   0.60 no     no                                    Chlorobenzene 19.00  4.30   2.00 no     no                                    Chloroform    17.80  3.10   5.70 no     no                                    Cyclohexanol  17.40  4.10   13.50                                                                              no     no                                    Diacetone alcohol                                                                           15.80  8.20   10.80                                                                              yes    --                                    o-dichlorobenzene                                                                           19.20  6.30   3.30 no     no                                    Diethylene glycol                                                                           16.20  14.70  20.50                                                                              yes    --                                    Diethyl ether 14.50  2.90   5.10 no     no                                    Dimemethyl formamide                                                                        17.40  13.70  11.30                                                                              yes    --                                    Dimethyl phthalate                                                                          18.60  10.80  4.90 no     yes                                   Dimethyl sulfoxide                                                                          18.40  16.40  10.20                                                                              yes    --                                    1,4-dioxane   19.00  1.80   7.40 no     no                                    Dipropylene glycol                                                                          15.90  20.20  18.40                                                                              no.sup.b                                                                             yes                                   Dipropylene glycol                                                                          15.50  5.70   11.20                                                                              yes    --                                    methyl ether                                                                  Ethanol       15.80  8.80   19.40                                                                              yes    --                                    Ethyl acetate 15.80  5.30   7.20 yes    --                                    Ethylene dichloride                                                                         19.00  7.40   4.10 no.sup.b                                                                             no.sup.b                              Hexane        14.90  0.00   0.00 yes    --                                    Isophorone    16.90  8.20   7.40 no     no                                    Methanol      15.10  12.30  22.30                                                                              yes.sup.a                                                                            --                                    Methylene chloride                                                                          18.20  6.30   6.10 yes    --                                    N--methyl-2-pyrro-                                                                          18.00  12.30  7.20 no     no                                    lidone                                                                        Nitrobenzene  20.00  8.60   4.10 yes.sup.a                                                                            --                                    2-nitropropane                                                                              16.20  12.10  4.10 yes    --                                    Propylene carbonate                                                                         20.00  18.00  4.10 yes    yes                                   Propylene glycol mono-                                                                      15.60  6.30   11.60                                                                              yes    --                                    methyl ether                                                                  Tetrahydrofuran                                                                             16.80  5.70   8.00 yes    --                                    Toluene       18.00  1.40   2.00 no     no                                    Trichloroethylene                                                                           18.00  3.10   5.30 no     no                                    ______________________________________                                         .sup.a Ought to have been within the calculated ball                          .sup.b Ought to have heen outside the calculated ball                    

EXAMPLE 5

Like in example 1, possible solvents for the printing ink "Sericol MV043" are selected on the basis of solubility tests and Hansenparameters.

The results obtained are listed in table 5:

                  TABLE 5                                                         ______________________________________                                        Solubility range for Sericol MV 043                                           δ.sub.D = 17.55 δ.sub.P = 10.30 δ.sub.H = 7.26 R.sub.P      = 6.93                                                                                             Solubility                                               Solvent       δ.sub.D                                                                        δ.sub.P                                                                        δ.sub.H                                                                      10 min.                                                                              24 hours                              ______________________________________                                        Acetone       15.50  10.40  7.00 yes    --                                    Acetophenone  19.60  8.60   3.70 yes    --                                    1,3-butane diol                                                                             16.60  10.00  21.50                                                                              no     no                                    1-butanol     16.00  5.70   15.80                                                                              no     no                                    Butyl acetate 15.80  3.70   6.30 yes.sup.a                                                                            --                                    γ-butyrolactone                                                                       19.00  16.60  7.40 yes.sup.a                                                                            --                                    Carbontetrachloride                                                                         17.80  0.00   0.60 no     no                                    Chlorobenzene 19.00  4.30   2.00 no     no                                    Chloroform    17.80  3.10   5.70 yes.sup.a                                                                            --                                    Cyclohexanol  17.40  4.10   13.50                                                                              no     no                                    Diacetone alcohol                                                                           15.80  8.20   10.80                                                                              no.sup.b                                                                             no.sup.b                              o-dichlorobenzene                                                                           19.20  6.30   3.30 no.sup.b                                                                             no                                    Diethylene glycol                                                                           16.20  14.70  20.50                                                                              no     no                                    Diethyl ether 14.50  2.90   5.10 yes    --                                    Dimemethyl formamide                                                                        17.40  13.70  11.30                                                                              no     no                                    Dimethyl phthalate                                                                          18.60  10.80  4.90 no     yes                                   Dimethyl sulfoxide                                                                          18.40  16.40  10.20                                                                              yes    --                                    1,4-dioxane   19.00  1.80   7.40 no     no                                    Dipropylene glycol                                                                          15.90  20.20  18.40                                                                              no     no                                    DipropyIene glycol                                                                          15.50  5.70   11.20                                                                              no     no                                    methyl ether                                                                  Ethanol       15.80  8.80   19.40                                                                              no     no                                    Ethyl acetate 15.80  5.30   7.20 no.sup.b                                                                             yes                                   Ethylene dichloride                                                                         19.00  7.40   4.10 no.sup.b                                                                             no                                    Hexane        14.90  0.00   0.00 yes    --                                    Isophorone    16.90  8.20   7.40 no     no                                    Methanol      15.10  12.30  22.30                                                                              yes    --                                    Methylene chloride                                                                          18.20  6.30   6.10 yes    --                                    N--methyl-2-pyrro-                                                                          18.00  12.30  7.20 yes    --                                    lidone                                                                        Nitrobenzene  20.00  8.60   4.10 yes    --                                    2-nitropropane                                                                              16.20  12.10  4.10 no     no                                    Propylene carbonate                                                                         20.00  18.00  4.10 no     no                                    Propylene glycol mono-                                                                      15.60  6.30   11.60                                                                              no     no                                    methyl ether                                                                  Tetrahydrofuran                                                                             16.80  5.70   8.00 yes    --                                    Toluene       18.00  1.40   2.00 no     no                                    Trichloroethylene                                                                           18.00  3.10   5.30 no     no.sup.b                              ______________________________________                                         .sup.a Ought to have been within the calculated ball                          .sup.b Ought to have been outside the calculated ball                    

EXAMPLE 6

Like in example 1, possible solvents for the printing ink Sericol"Polyplast PY-043" are selected on the basis of solubility tests andHansen parameters.

The results obtained are listed in table 6:

                  TABLE 6                                                         ______________________________________                                        Solubility range for Sericol "Polyplast PY-043"                               δ.sub.D = 19.37 δ.sub.P = 8.73 δ.sub.H = 5.91 R.sub.P =     8.74                                                                                               Solubility                                               Solvent       δ.sub.D                                                                        δ.sub.P                                                                        δ.sub.H                                                                      10 min.                                                                              24 hours                              ______________________________________                                        Acetone       15.50  10.40  7.00 yes    --                                    Acetophenone  19.60  8.60   3.70 yes    --                                    1,3-butane diol                                                                             16.60  10.00  21.50                                                                              no     no                                    1-butanol     16.00  5.70   15.80                                                                              no     no                                    Butyl acetate 15.80  3.70   6.30 yes    --                                    γ-butyrolactone                                                                       19.00  16.60  7.40 yes    --                                    Carbontetrachloride                                                                         17.80  0.00   0.60 no     no                                    Chlorobenzene 19.00  4.30   2.00 yes    --                                    Chloroform    17.80  3.10   5.70 yes    --                                    Cyclohexanol  17.40  4.10   13.50                                                                              no     no.sup.b                              Diacetone alcohol                                                                           15.80  8.20   10.80                                                                              no.sup.b                                                                             yes                                   o-dichlorobenzene                                                                           19.20  6.30   3.30 yes    --                                    Diethylene glycol                                                                           16.20  14.70  20.50                                                                              no     no                                    Diethyl ether 14.50  2.90   5.10 no     no                                    Dimemethyl formamide                                                                        17.40  13.70  11.30                                                                              yes    --                                    Dimethyl phthalate                                                                          18.60  10.80  4.90 no     yes                                   Dimethyl sulfoxide                                                                          18.40  16.40  10.20                                                                              yes.sup.a                                                                            --                                    1,4-dioxane   19.00  1.80   7.40 yes    --                                    Dipropylene glycol                                                                          15.90  20.20  18.40                                                                              no     no                                    Dipropylene glycol                                                                          15.50  5.70   11.20                                                                              no     no                                    methyl ether                                                                  Ethanol       15.80  8.80   19.40                                                                              no     no                                    Ethyl acetate 15.80  5.30   7.20 yes    --                                    Ethylene dichloride                                                                         19.00  7.40   4.10 yes    --                                    Ethylene glycol mono-                                                                       15.90  4.70   10.60                                                                              yes    --                                    ethyl ether acetate                                                           Hexane        14.90  0.00   0.00 no     no                                    Isophorone    16.90  8.20   7.40 no.sup.b                                                                             yes                                   Methanol      15.10  12.30  22.30                                                                              no     no                                    Methylene chloride                                                                          18.20  6.30   6.10 yes    --                                    N--methyl-2-pyrro-                                                                          18.00  12.30  7.20 yes    --                                    lidone                                                                        Nitrobenzene  20.00  8.60   4.10 yes    --                                    2-nitropropane                                                                              16.20  12.10  4.10 yes    --                                    Propylene carbonate                                                                         20.00  18.00  4.10 no     yes                                   Propylene glycol mono-                                                                      15.60  6.30   11.60                                                                              no     no                                    methyl ether                                                                  Tetrahydrofuran                                                                             16.80  5.70   8.00 yes    --                                    Toluene       18.00  1.40   2.00 no     no                                    Trichloroethylene                                                                           18.00  3.10   5.30 yes    --                                    ______________________________________                                         .sup.a Ought to have been within the calculated ball                          .sup.b Ought to have been outside the calculated ball                    

It appears from the foregoing examples that there are several solventcandidates for each individual printing ink which are within thesolubility range according to the Hansen model, but which are

(a) not useful in practice because of current environmentalrequirements,

(b) not useful in practice because of too slow dissolution effect, cf.the time parameter previously mentioned, or

(c) have no effect on one or more of the ordinary printing inks.

EXAMPLE 7

This example shows that the solvent mixtures EX I A, EX I B, EX I C andEX 2 destroy the glue system more than the liquid mixtures O and V ofthe invention. It is moreover shown that a too large amount ofγ-butyrolactone in the liquid mixtures of the invention (above 25%)destroys the glue system.

The commercial glue systems used were the following:

1. 10% hardener, as prescribed by the manufacturer

2. 10% hardener, as prescribed after 24 hours' hardening, coated withlacquer so that all the glue is covered.

3. 20% hardener, the frame having been pre-coated with a glue mixturewhich has hardened for 24 hours before mounting of the screen.

    ______________________________________                                        Solvent mixtures                                                                   WW %                                                                     ______________________________________                                        EX I                                                                          A    75.72      N--methyl-2-pyrrolidone                                            18.52      Ethylene glycol monobutyl ether                                     3.04      Cyclohexanone                                                       2.72      Synperonic NP 9                                               EX I                                                                          B    47.12      N--methyl-2-pyrrolidone                                       B    47.12      Ethylene glycol monobutyl ether                                     3.04      Cyclohexanone                                                       2.72      Synperonic NP 9                                               EX I                                                                          C    39.38      N--methyl-2-pyrrolidone                                            18.52      Ethylene glycol monobutyl ether                                    39.38      Cyclohexanone                                                       2.72      Synperonic NP 9                                               EX 2                                                                               37.86      N--methyl-2-pyrrolidone                                             9.26      Ethylene glycol monobutyl ether                                     1.52      Cyclohexanone                                                      24.00      Ethylene glycol monoethyl ether acetate                            26.00      Methylene chloride                                                  1.36      Synperonic NP 9                                               ______________________________________                                        Liquid mixture V of the invention with various amounts                        of γ-butyrolactone                                                                     V        V.sub.C                                                              W/W %    W/W %                                                 ______________________________________                                        Isoper L       24.9     23.7                                                  DMP            16.6     15.8                                                  MPA            41.5     39.8                                                  γ-butyrolactone                                                                        11.3     15.0                                                  Synperonic NP 9                                                                               5.9      5.7                                                  ______________________________________                                        A maximum of 15 W/W γ-butyrolactone may be added if                     a homogenous liquid is desired.                                               ______________________________________                                        Liquid mixture V with various amounts of N--methyl-2-                         pyrrolidone                                                                              V.sub.A      V.sub.D   F.sub.F                                                W/W %        W/W %    W/W %                                        ______________________________________                                        Isoper L   24.9         22.29    20.79                                        DMP        16.6         14.86    13.86                                        MPA        41.5         37.15    34.65                                        N--methyl-2-                                                                             11.3         20.0     25.0                                         pyrrolidone                                                                   Synperonic NP 9                                                                           5.7          5.7      5.7                                         ______________________________________                                        Liquid mixture V with various amounts of γ-butyrolactone                and N--methyl-2-pyrrolidone                                                                  V.sub.B  V.sub.E                                                              W/W %    W/W %                                                 ______________________________________                                        Isoper L       24.9     20.29                                                 DMP            16.6     14.86                                                 MPA            41.5     37.15                                                 γ-butyrolactone                                                                        5.65     10.0                                                  N--methy1-2-                                                                  pyrrolidone                                                                   Synperonic NP 9                                                                              5.7      5.7                                                   ______________________________________                                        Liquid mixture O with various amounts of γ-butyrolactone                               O          O.sub.I  O.sub.L                                                   W/W %      W/W %    W/W %                                      ______________________________________                                        Isoper L       9.7        8.95     8.37                                       PMA            14.6       13.48    12.61                                      DB             27.2       25.12    23.49                                      DPM            32.0       29.55    27.63                                      γ-butyrolactone                                                                        13.6       20.0     25.0                                       Synperonic NP 9                                                                              2.9        2.9      2.9                                        ______________________________________                                        Liquid mixture O with various amounts of N--methyl-2-pyrrolidone                             O.sub.G    O.sub.J  O.sub.M                                                   W/W %      W/W %    W/W %                                      ______________________________________                                        Isoper L       9.7        8.95     8.37                                       PMA            14.6       13.48    12.61                                      DB             27.2       25.12    23.49                                      DPM            32.0       29.55    27.63                                      N--methyl-2-pyrrolidone                                                                      13.6       20.0     25.0                                       Synperonic NP 9                                                                              2.9        2.9      2.9                                        ______________________________________                                        Liquid mixture O with various amounts of γ-butyrolactone                and N--methyl-2-pyrrolidone                                                                  O.sub.H    O.sub.K  O.sub.N                                                   W/W %      W/W %    W/W %                                      ______________________________________                                        Isoper L       9.7        8.95     8.37                                       PMA            14.6       13.48    12.61                                      DB             27.2       25.12    23.49                                      DPM            32.0       29.55    27.63                                      γ-butyrolactone                                                                        6.8        10.0     12.5                                       N--methyl-2-pyrrolidone                                                                      6.8        10.0     12.5                                       Synperonic NP 9                                                                              2.9        2.9      2.9                                        ______________________________________                                         Synperonic NP 9 = Surfactant.                                                 Isoper L = Solvent, flash point 64° C.                            

    __________________________________________________________________________    Test results                                                                  Glue system                                                                            1.          2.           3.                                          time (hours)                                                                           1.5 h                                                                             2.5 h                                                                             3.5 h                                                                             1.5 h                                                                              2.5 h                                                                              3.5 h                                                                             1.5 h                                                                            2.5 h                                                                             3.5 h                               __________________________________________________________________________    Pregan 240 E                                                                            0   0  0-1 -1-0 -1-0  0   0  0  0-1                                 V         6  8-9  8  5     4    5   4 6-7  6                                  V.sub.A 11.3% NM2P                                                                      8   9  10-11                                                                              6    5   6-7 5-6                                                                              7-8 7-8                                 V.sub.B 11.3% NM2P/                                                                    7-8 10  10   6    6    6   6  8  7-8                                 BLO                                                                           V.sub.C 15% BLO                                                                        6-7 11-12                                                                             12   7   10-11                                                                              11   6  8   7                                  V.sub.D 20% NM2P                                                                       13  13-14                                                                             14-15                                                                             11   13   10   9 12  12                                  V.sub.E 20% NM2P/                                                                      7-8 13-14                                                                             12   9   12   10  10 10- 11                                                                            12                                  BLO                                                                           V.sub.F 25% NM2P                                                                       13-14                                                                             13-14                                                                             12  14   14   11-12                                                                             12 12                                      O 14% BLO                                                                              4-5  7  6-7  2    3   5-6  4 5-6 4-5                                 O.sub.G 14% NM2P                                                                       3-4  8  6-7  2    4   5-6  4  6  4 5                                 O.sub.H 14% NM2P/                                                                       9   8   2   4   6-7   5   5  6                                      BLO 4-5                                                                       O.sub.I 20% BLO                                                                         6   8  11-12                                                                             4-5   4   6-7  4 5-6 5-6                                 O.sub.J NM2P                                                                            8   9  11   3   4-5   6   5 8-9 8-9                                 O.sub.K NM2P/BLO                                                                        7  8-9 11   3    4    7  5-6                                                                              8-9  7                                  O.sub.L 25% BLO                                                                         7   6  11   3    6    6  4-5                                                                               6   7                                  O.sub.M 25% NM2P                                                                       8-9 11  10  4-5   6    6  6-7                                                                               9   9-10                               O.sub.N 25% NM2P/                                                                      6-7 12  12  4-5   6    8   6  9   8                                  BLO                                                                           EX I A   11  14  15  +*   *    *    16*                                                                             *   16                                  EX I B   12  14  15   9+  14   14  14 15  15                                  EX I C   13  13  14-15                                                                             13+  14-15                                                                              *   14 14-15                                                                             15                                  EX 2     14  14  14  14+  14-15                                                                              15  14 15  15                                  __________________________________________________________________________     +dissolves the lacquer                                                         *falls off                                                                   the higher the figure, the more the glue system is destroyed.                 14-15 inacceptable                                                            V contains 11.3% butyrolactone (BLO)                                          O contains 13.6% butyrolactone                                                NM2P = N--methyl2-pyrrolidone                                            

It appears from the results that EX I A, EX I B, EX I C and EX 2 destroyall three glue systems, and that destruction of the glue systemsincreases with increasing addition of γ-butyrolactone andN-methyl-2-pyrrolidone, respectively, to the liquid mixtures O and V ofthe invention.

We claim:
 1. A liquid for removing printing and screen printing inks, characterized by consisting of an essentially anhydrous mixture comprising(a) γ-butyrolactone and/or N-methyl-2-pyrrolidone in an amount of 1-25% v/v) as well as (b) one or more propylene glycol derivatives selected from substituted propyl acetates of the formula ##STR5## wherein R is hydrogen or alkyl having from 1 to 6 carbon atoms, and/or propylene glycol ethers of the formula ##STR6## wherein R₁ is alkyl having from 1 to 6 carbon atoms, and n is 1, 2 or 3, and optionally (c) a diluent selected from aliphatic compounds having a flash point above 22° C. and a content of aromatic compounds below 1% and/or (d) a surfactant, the amount of components (b), (c) and (d) constituting 99-75% (v/v) of the liquid.
 2. A liquid according to claim 1,characterized in that R is methyl or ethyl.
 3. A liquid according to claim 1 or 2,characterized in that it contains as component (b) one or more propylene glycol ethers selected from propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether and tripropylene glycol monomethyl ether.
 4. A liquid according to claim 3, characterized in that it contains as diluent one or more aliphatic hydrocarbons and/or an ether selected from butyl diglycol ether, ethyl diglycol ether and methyl diglycol ether.
 5. A liquid according to, claim 4, characterized in that it contains a surfactant.
 6. A liquid according to claim 1,characterized in that it consists of

    1-25% of component (a)

    up to 99% of component (b)

and 0-91% of component (c), optionally containing component (d).
 7. A liquid according to claim 1, characterized in that the amount of components (c) and (d) together constitutes up to 50% of the mixture.
 8. A liquid according to claim 1 or 2, characterized in that it contains as diluent one or more aliphatic hydrocarbons and/or an ether selected from butyl diglycol ether, ethyl diglycol ether and methyl diglycol ether.
 9. A liquid according to claim 3 characterized in that it contains a surfactant.
 10. A liquid according to claim 9, characterized in that the surfactant is in the form of a nonyphenol ethoxylate.
 11. A liquid according to claim 1 or 2 characterized in that it contains a surfactant.
 12. A liquid according to claim 1, characterized in that it contains about 10% (v/v) of component (a).
 13. A liquid according to claim 1, characterized in that it contains a surfactant in the form of a nonylphenol ethoxylate. 